Moored mines are mines of neutral buoyancy being attached by a cable, called tether, to an anchor, called sinker, resting on the seabed. The sonars are mounted either on a surface ship, or on a fish towed by a surface ship or on a self-propelled underwater vehicle.
One of the problems in detecting objects having neutral buoyancy is being able to detect mines over a wide swath so as to monitor an area of the marine environment that is as wide as possible in a minimum time. Another problem is being able to locate the detected mines with a sufficiently great accuracy in the three dimensions of space. In other words, another problem is producing a system for detecting underwater objects that exhibits a sufficient locating accuracy in the three dimensions of space of the order of a few meters.
One existing solution consists in using front looking sonars which insonify the water column in front of the carrier and which form a plurality of contiguous directional beams in reception terms. One drawback with this solution is that, to cover a wide swath at right angles to the axis of the carrier and locate underwater targets having neutral buoyancy with a good accuracy in terms of relative bearing, arrays that are of large dimensions, are bulky and consume a lot of electrical energy are needed. This drawback is incompatible with the trend in mine warfare which is to distance man from the threat. Technical solutions are sought for mounting the sonars on autonomous carriers, on board which a limited energy is stored, rather than on ships of mine hunter type. Another drawback with front looking sonars is that they do not make it possible to locate the mines with a good accuracy in terms of elevation without an array that is directional in elevation and which therefore adds bulk and energy consumption.
Another solution is described in patent application U.S. Pat. No. 5,506,812; it consists in using cylindrical emission and reception arrays that make it possible to insonify a toroidal zone surrounding the carrier in a single acoustic ping, that is to say a single acoustic pulse. This solution presents the drawbacks of requiring a high emission power to transmit an acoustic pulse over 360° and of being very bulky since it uses an array with 120 reception channels. Moreover, the processing of the multiple reception channels to detect objects in the water column and locate them can prove complex.